The animal hospital's affiliated kennel, Cape Cod Farm Kennels, will require the vaccine for all boarding dogs as of February, McMorrow said.

About 80 dogs have received at least one flu shot within the past two weeks, she said.

Dogs initially require two shots of vaccine two to four weeks apart and then an annual booster. The cost is about $20 per shot.

First identified in 2004 after an outbreak among racing greyhounds, the virus is still so new that about 80 percent of exposed dogs get sick.

"Dogs have no natural immunity to influenza whatsoever," said Thomas Burns, veterinarian with Veterinary Associates of Cape Cod in South Yarmouth.

"All it takes is one dog in a kennel" to get sick to cause an outbreak, said veterinarian Claire Sharp, an assistant professor at the Cummings School of Veterinary Medicine at Tufts University.

The virus has been reported in Massachusetts in companion animals and in greyhounds in 2005, she said.

According to media reports, the animal virus also has broken out in New York, New Jersey, Connecticut, Colorado and Texas.

Flu symptoms in dogs are similar to those of a head cold in people. Fido may cough, sneeze, run a low-grade fever and experience discharge around the nose and eyes.

"For most dogs it's a very mild disease," Burns said.

The risk of an outbreak is too high for Cape Cod Farm Kennels, which can board up to 80 dogs at a time, McMorrow said.

Dogs start "shedding" the virus before they show symptoms, she said, which increases the risk of dog owners taking infected canines to places where other dogs congregate.

Pet groomers and other animal handlers also can pass along the virus on their clothing, Sharp said.

"The virus actually can live on our clothes," she said. "It can live for a couple of days on inanimate objects."

Approximately 5 to 8 percent of dogs exposed to the virus will die, Sharp said.

The relatively low mortality rate means the vaccine "wouldn't be warranted for all dogs," said Lynne White-Shim, a veterinarian and assistant director with the division of scientific activities at the American Veterinary Medical Association in Schaumburg, Ill.

"It's really based on the benefit-risk to a particular dog," she said.

For dogs that spend time near other dogs in kennels, doggie day care and socialize heavily at dog parks the vaccine would be a "good idea," Burns said.

Veterinarians say they are not aware of any outbreaks of H3N8 on the Cape.

At the Animal Inn boarding facility in Forestdale, manager Jim Shea said staff members are leaving the decision about vaccinating against the flu to dog owners and their veterinarians.

There is no requirement that pets be immunized against the flu, he said.